The label on the door of my car has the pressures for these tyres displayed also, iirc 32 psi at the front and 35psi at the back. Same size tyre all round so why it's different front and rear, I'm not sure. Must be to do with some physics or something else I don't understand, lol

Be aware as well that BMW's tyre pressure recommendation varies from M3 to M3 i.e. the tyre pressure for an M3 Coupe might be different to another M3 coupe. Reason for this is due to varying weights due to varying options on each vehicle. This is the same reason why there are many different oem springs for each M3 version (coupe, sedan and convertible) i.e. the springs on a M3 Coupe Manual are different to the springs on a M3 Coupe DCT. Basically, what I'm trying to say is to follow what is written on your pressure placard as those pressures are specific to your car. If you don't have the placard, best contact your dealer for a replacement specific to your VIN.

This is my pressure sticker. They don't mention 235/40/18's and no mention of M&S tyres. It's a 2012 Coupe DCT with Competition Pack.

BMW updated the winter tyres for the M3 Competition pack and are suppose to have 245/40 R18 winter tyres unlike the earlier 235/40 R18. But there's no harm in using the tyre pressure indicated for the 245/40 R18 on your 235/40 R18.

Edit: I've just checked my placard, which is also the comp pack version, and it's also 245/40 R18 for winter tyres. I believe it's 245 to help with ground clearance given that the comp pack is 10mm lower and using a 45 profile with 235 section would be too tall a tyre, while 235/40 would obviously be too low for the comp pack.

BMW updated the winter tyres for the M3 Competition pack and are suppose to have 245/40 R18 winter tyres unlike the earlier 235/40 R18. But there's no harm in using the tyre pressure indicated for the 245/40 R18 on your 235/40 R18.

Edit: I've just checked my placard, which is also the comp pack version, and it's also 245/40 R18 for winter tyres. I believe it's 245 to help with ground clearance given that the comp pack is 10mm lower and using a 45 profile with 235 section would be too tall a tyre, while 235/40 would obviously be too low for the comp pack.

Interesting! Seeing as these are new set of wheels and tyres I would have liked to have been sold the correct set!